The present invention relates generally to CMOS (complementary metal-oxide-semiconductor) current-controlled and voltage-controlled oscillators wherein the frequency of oscillation is varied by changing an applied current or voltage, respectively, and, more particularly, to CMOS integrated circuits useful in constructing high speed current-controlled and voltage-controlled oscillators by interconnection of an odd plurality of oscillator cells, preferably three oscillator cells, into a ring configuration.
Current-controlled and voltage-controlled oscillators are widely used in both digital and analog systems to generate periodic waveforms having precisely controlled frequencies. Oftentimes, such oscillators are incorporated into phase-locked loops (PLLs) to provide phase and frequency tracking for the PLLs. One specific application for a PLL incorporating a current-controlled or voltage-controlled oscillator is a PLL clock generator which is used to generate a fast on-chip clock from a slower off-chip system clock.
When implemented utilizing bipolar or GaAs (gallium arsenide) technology, prior art current-controlled and voltage-controlled oscillators are capable of operating at frequencies beyond Ghz. However, when implemented using low cost CMOS technology, the maximum operating frequencies of known current-controlled and voltage-controlled oscillator circuits are substantially lower due in part to smaller transconductances which are inherent in MOS devices.
The use of sub-micron CMOS technology having improved transistor transconductances has increased the operating speed of many CMOS circuits such that they can be used in applications which previously required bipolar or GaAs devices. Unfortunately, known prior art CMOS current-controlled and voltage-controlled oscillator designs, even when implemented in sub-micron CMOS technology, fail to provide a useful frequency range approaching 1 Ghz.
Accordingly, there is a need for an improved design for CMOS current-controlled and voltage-controlled oscillator circuits which perform within such a higher frequency range.